Urban adaptation strategies, such as "green roofs" or "cool roofs," are being tried as ways to cope with climate change, be it from greenhouse gas emissions or city expansion, but their effectiveness varies based on location.

A new study finds that these measures are effective in offsetting or counteracting the effects of city growth and global warming due to greenhouse gases, but there needs to be careful planning for them to work.

The study, led by Matei Georgescu of Arizona State University, uses simulations to determine the effectiveness of different urban adaptation strategies based on location. For example, the effectiveness of a cool roof, painting the roof white to reflect the sun and reduce indoor temperatures during the summer, in Florida versus using a cool roof in California.

Georgescu and his team discovered there is no “universal solution” to countering climate change and reducing the effects of city expansion and warming due to greenhouse gas emissions. The simulations revealed that, while cool roofs reduced temperatures during the summer, thus cutting the need for air conditioners, the white paint also reduces temperatures in the winter, which means more energy needs to be used.

“The energy savings gained during the summer season, for some regions, is nearly entirely lost during the winter season," Georgescu said in a statement.

Cool roofs can also affect precipitation, based on the simulations for Florida and other Southern states. According to Georgescu, cool roofs can lead to a “2 to 4 millimeter per day reduction in rainfall” that would affect water availability and the local ecosystem.

Careful planning and understanding the effects of certain urban adaptation strategies could lead to more effective strategies. The researchers say that without urban adaptation, city expansion alone will result in a 3 degree Celsius (6 degrees Fahrenheit) increase in surface temperature and cool roofs as well as green roofs are viable solutions to the problem, but each city is different and location must be factored into each decision.

The authors said in a statement, “Judicious planning and design choices can not only counteract rising temperatures due to increasing urban sprawl but also offset a significant portion of anticipated greenhouse gas-driven warming, at scales that extend beyond individual cities to large swaths of the country.” The study was published in the Proceedings of the National Academy of Sciences of the United States of America.

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